add peeranha link

Author: wolovim

pages/lessons/projects/3.mdx

@@ -21,7 +21,7 @@ import { LessonHeader } from '../../../components/mdx/LessonHeader'
 
 <LessonHeader 
 title="Lesson 3: Tier NFTs" 
-discussionUrl="https://developerdao.peeranha.io/discussions"
+discussionUrl="https://developerdao.peeranha.io/discussions/1641/creating-a-smart-contract-for-%E2%80%98tiered%E2%80%99-nfts"
 />
 ## About this lesson